1. Field of the Invention
This invention relates to filtration apparatus having a filter cloth, particularly for filtering water containing solid material which collects as a sludge on the cloth. The apparatus may comprise a plurality of filter elements.
2. Description of the Prior Art
NL-A-8802292 describes a filtration system comprising at least one filter element which at least on one side is provided with a filter cloth through which water to be filtered is sucked. The filter cloth is provided on its downstream side in the normal filtration direction with means for supporting it against the pressure difference. The filter cloth is provided on its upstream side with means for removing the sludge collected on the filter cloth. The sludge collected on the filter cloth is removed in the course of time by reversal of the direction of flow of water so that the filter cloth billows out from the support means, whereupon a scraper is moved along the billowed out filter cloth to remove the sludge.
A problem with this known apparatus is that the reverse flow through the filter cloth only leads to local loosening of the sludge layer. This is believed to occur because the reverse flow finds the path of least resistance, so that if locally some sludge is loosened, there is insufficient pressure remaining for removing the sludge from the filter cloth elsewhere as well.